Calculator Android App

A precision-focused Android calculator with dual portrait/landscape layouts (basic & scientific) and arbitrary-precision arithmetic using BigDecimal. Written entirely in Kotlin.

Quick Start

• build: make build
• install: make install
• launch: make launch
  • build, install and launch app

Prerequisites

• JDK 17 or higher
• Android SDK 21+ (minimum API level)
• Android build tools 35+

Using Android Studio

1. Open the project in Android Studio
2. Click Run or press Shift + F10 to build and launch on an emulator or device

Basic Calculator (Light)	Basic Calculator (Dark)

Scientific Calculator

Light

Dark

Features

• BigDecimal precision arithmetic — uses EvalEx for exact decimal calculations (no floating-point rounding errors)
• Reverse Polish Notation (RPN) evaluation for reliable expression parsing
• Dual-mode UI — basic four-function calculator in portrait, full scientific calculator in landscape
• Modern Android stack — Kotlin, AndroidX, Material Design compatible
• Unit tested — includes parameterized JUnit tests for calculation validation

Architecture

The app uses a single-Activity design. MainActivity is a thin UI layer that wires button clicks to CalculatorEngine and renders its state; all calculation logic and state live in CalculatorEngine, which delegates expression evaluation to EvalEx.

Key Components

• CalculatorEngine (app/src/main/java/com/example/calculator_v01/CalculatorEngine.kt) — state machine for calculator input/eval, EvalEx integration
• MainActivity (app/src/main/java/com/example/calculator_v01/MainActivity.kt) — button handlers and rendering only, no calc logic
• Layouts — activity_main.xml (portrait) and layout-land/activity_main.xml (landscape)
• Tests — CalculatorEngineTest.kt (state behavior) and CalculatorEvalTest.kt (parameterized arithmetic evaluation)

Build Information

Property	Value
Gradle	8.7+
AGP (Android Gradle Plugin)	8.5+
Kotlin	2.0.0
Compile SDK	35
Min SDK	21
Target SDK	35
Java/Kotlin JVM	17

Acknowledgments

• EvalEx — expression evaluation library with BigDecimal precision
• Android Developers — comprehensive Android documentation